[PATCH] random: overflow fix

Zwane reports an oops duie to add_entropy_words running off the top of the
stack reading its input.  The overrun is harmless until it causes a page
fault.

Looks like I introduced this bug in Aug 2003, but it was hard to trigger until
the recent changes.
Signed-off-by: Matt Mackall <mpm@selenic.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

drivers/char/random.c

@@ -1322,7 +1322,7 @@ static inline void xfer_secondary_pool(struct entropy_store *r,
 
 		bytes=extract_entropy(random_state, tmp, bytes,
 				      EXTRACT_ENTROPY_LIMIT);
-		add_entropy_words(r, tmp, bytes);
+		add_entropy_words(r, tmp, (bytes + 3) / 4);
 		credit_entropy_store(r, bytes*8);
 	}
 }